Discovery of alkenones with variable methylene‐interrupted double bonds: implications for the biosynthetic pathway

Alkenones (C₃₇–C₄₀) are highly specific biomarkers produced by certain haptophyte algae in ocean and lacustrine environments and have been widely used for paleoclimate studies. Unusual shorter‐chain alkenones (SCA; e.g., C₃₅ and C₃₆) have been found in environmental and culture samples, but the origin and structure of these compounds are much less understood. The marine alkenone producer, Emiliania huxleyi CCMP2758 strain, was reported with abundant C_35:2Me (?^{12, 19}) alkenones when cultured at 15°C (Prahl et al. 2006). Here we show, when this strain is cultured at 4°C–10°C, that CCMP2758 produces abundant C_35:3Me, C_36:3Me, and small amounts of C_36:3Et alkenones with unusual double‐bond positions of ?^{7, 12, 19}. We determine the double‐bond positions of the C_35:3Me and C_36:3Me alkenones by GC‐MS analysis of the dimethyl disulfide and cyclobutylamine derivatives, and we provide the first temperature calibrations based on the unsaturation ratios of the C₃₅ and C₃₆ alkenones. Previous studies have found C_35:2Me (?^{14, 19}) and C_36:2Et (?^{14, 19}) alkenones with three‐methylene interruption in the Black Sea sediments, but this is the first reported instance of alkenones with a mixed three‐ and five‐methylene interruption configuration in the double‐bond positions. The discovery of these alkenones allows us to propose a novel biosynthetic scheme, termed the SCA biosynthesis pathway, that simultaneously rationalizes the formation of both the C_35:3Me (?^{7, 12, 19}) alkenone in our culture and the ?^{14, 19} Black Sea type alkenones without invoking new desaturases for the unusual double‐bond positions.     

Alkenone and alkenoic acid compositions of the membrane fractions of Emiliania huxleyi

The lipid classes and unsaturation ratios of long-chain alkenones (nC37-C39), related alkyl alkenoate compounds (nC37-C38) and alkenoic acids (nC14-C22) were determined in isolated membrane and organelle fractions of Emiliania huxleyi. The percentage distribution of these compounds was predominantly high in the endoplasmic reticulum (ER) and coccolith-producing compartment (CPC)-rich membrane fraction, although alkenones and alkenoates could be detected in all membrane fractions. In particular, the alkenones were mainly located in CPC, since their distribution was closely correlated with that of uronic acids which are markers of CPC. In contrast, the alkenoic acids seemed to be mainly located in chloroplast (thylakoid)-rich fractions. The alkenone unsaturation ratio and the ratio of alkenoates to alkenones were similar in all fractions, while the unsaturation ratio of alkenoic acids in the thylakoid-rich and plasma membrane (PM)/Golgi body-rich fractions was overwhelmingly higher than that in the ER/CPC-rich fractions. Thus, alkenoic acids seemed to be typical membrane-bound lipids, and could be closely related to photosynthesis and involved in regulating membrane fluidity and rigidity in E. huxleyi. It is presumed from these results that the alkenones and alkenoates were membrane-unbound lipids that might be associated with the function of CPC.     

Liquid-Saturated Hydrocarbons Resulting from Pyrolysis of the Marine Coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica

Two nanoplanktonic marine coccolithophores, Emiliania huxleyi and Gephyrocapsa oceanica, were grown at 23°C with a 16-hour light and 8-hour darkness regimen. The cells were dried at room temperature and then subjected to pyrolysis at 100° to 500°C under anoxygenic conditions to produce hydrocarbons. Temperature-dependent profiles of the liquid-saturated hydrocarbons (saturates) produced during pyrolysis were very similar for the two strains, although the total amount was higher in E. huxleyi than in G. oceanica. The amount of saturates produced was only 0.05% to 0.15% below 200°C, but about 2.1% to 2.8% at 300°C. Their major components were normal alkanes in a series ranging from nC₁₁ to nC₃₅ with the predominant peak at nC₁₅. At 400° and 500°C most of saturates transformed into gaseous compounds. The major saturates identified in all pyrolysates were normal C₃₁ monounsaturated and diunsaturated alkenes, a series of normal alkanes, phytenes, C₂₈ sterenes, and steranes. Profiles of saturates in gas chromatography–mass spectroscopy varied with increasing pyrolysis temperature and also differed between E. huxleyi and G. oceanica. The two coccolithophores are useful candidates for the production of renewable liquid fuel through pyrolysis—especially E. huxleyi, which has higher production. The results also provide information for further studies on the characterization, source, and paleogeographic distribution of marine sediment. Received October 28, 1998; accepted February 15, 1999     

The effect of growth temperature on the long-chain alkenes composition in the marine coccolithophorid Emiliania huxleyi

The hydrocarbon fraction of a pure culture of Emiliania huxleyi, composed of a mixture of C31, C33, C37 and C38 polyunsaturated n-alkenes, appeared strongly dependent on the growth temperature of the alga between 8 degrees C and 25 degrees C. The total hydrocarbon content increased linearly with decreasing temperatures. C37 and C38 alkenes (which accounted for more than 90% of the total hydrocarbons) showed distinct changes in distribution compared to C31 and C33 alkenes, suggesting different biological syntheses and/or functions for these two groups of compounds. C37 and C38 alkenes and C37 methyl ketones (alkenones) all showed a trend to lower proportions of the two diunsaturated isomers and to higher proportions of the corresponding trienes with decreasing temperature. Unlike the alkenone unsaturation ratio (U37k'), ratios based on the C37 and C38 alkadi- and trienes could be linearly related to the growth temperature of E. huxleyi only between 15 degrees C and 25 degrees C. The modifications in the distribution of alkenes induced by varying temperature appeared, however, to be twice as fast as the modifications undergone by the alkenones. Although structurally and biochemically related, the distinct evolutions of alkenes and alkenones in response to changes in growth temperature might indicate that these two classes of compounds play two distinct physiological functions. The non-systematic linearity of relationships to temperature of parameters based on alkenes distribution suggested that these compounds are of limited use as paleotemperature indicator in the marine environment in contrast with the alkenones.     

Phylogenetic diversity in freshwater‐dwelling Isochrysidales haptophytes with implications for alkenone production

Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of alkenones, long‐chain ketones that are commonly used for paleotemperature reconstructions. Alkenone‐producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri‐unsaturated alkenone isomers (C_37:3b Me, C_38:3b Et, C_38:3b Me, C_39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small‐subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high‐throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well‐supported clade separating the previously described “EV” clade from the “Greenland” clade. We infer the first partial large‐subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well‐supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri‐unsaturated alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on alkenone biosynthesis.     

PHOTOSYNTHETIC CHARACTERISTICS OF THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) EXPOSED TO ELEVATED CONCENTRATIONS OF DISSOLVED INORGANIC CARBON1

Light-saturated photosynthesis (P_max) of Emiliania huxleyi (Lohmann) Hay et Mohler is known to be carbonlimited at natural concentrations of dissolved inorganic carbon (DIC). In the present study, light-limited and light-saturated photosynthetic rates of E. huxleyi were studied at three concentrations of DIC (2.4, 7.4, and 12.4 mM) for high-calcite (C_in/C_tot=0.48) and low-calcite (C_in/C_tot=0.08) cells of the same strain. The photosynthetic efficiency (α) and the maximum quantum yield (θ_max)A increased by more than a factor of 2 from the lowest to the highest DIC level. P_max a, and θ_max were always higher for the high-calcite than for the low-calcite cells at identical DIC levels. This may indicate that the calcifcation process acts as an extra supplier of CO₂ for photosynthesis making the CO₂ shortage at natural DIC levels a little smaller for high-calcite than for low-calcite E. huxleyi. A dependency of θ_max on DIC has not previously been shown for marine phytoplankton. θ_max is a key parameter in recent biooptical models of phytoplankton productivity, and the results from the present study are therefore important for modeling the productivity of E. huxleyi.     

Alleviation of Toxicity of Poisonous Organic Compounds on Hydrophilic Carrier/Hydrophobic Organic Solvent Interface

Growth tests of type culture strains were done on interfaces between nutrient agar and hydrophobic organic solvents. All strains examined were able to grow against n-paraffin (C₁₁-C₁₅), and many could grow against isooctane, and pentyl- and heptylbenzene. The interface cultivation method was also successful even when the solvent layer contained compounds toxic for microorganism.     

Paenibacillus tylopili sp.nov., a chitinolytic bacterium isolated from the mycorhizosphere of Tylopilus felleus

Two chitinolytic bacterial strains (designated MK2^T and V7) were isolated from the mycorhizosphere of the fungus Tylopilus felleus. The strains were facultatively anaerobic G⁺ endospore formers. Physiological analysis and 16S rRNA gene PCR-RFLP assays revealed nearly identical profiles for both strains, demonstrating their relationship at the species level. Sequences specific for the genus Paenibacillus were found within the 16S rRNA gene sequence of the strain MK2^T. The 16S rRNA gene sequence showed the highest similarity to the sequences of Paenibacillus amylolyticus, P. pabuli and P. xylanilyticus. DNA-DNA relatedness of the strain with the type strain of P. amylolyticus was 4.95 %, of P. pabuli 38.0 %, and of P. xylanilyticus 46.3 %, indicating no relatedness between MK2^T and any of them at the species level. The most abundant fatty acids in strains MK2^T and V7 were anteiso-C_15:0, iso-C_16:0, iso-C_15:0 and n-C_16:0. DNA-DNA relatedness, morphological, physiological and chemotaxonomic analyses, and phylogenetic data based on 16S rRNA gene sequencing made it possible to describe both strains as the novel species of the genus Paenibacillus, for which the name Paenibacillus tylopili is proposed, the type strain being MK2^T (DSM 18927^T, LMG 23975^T).     

Reduction chemistry of the mixed ligand metallocene [(C5Me5)(C8H8)U]2(μ-C8H8) with bipyridines

The U⁴⁺ cyclooctatetraenyl complex, [(C₅Me₅)(C₈H₈)U]₂(μ-C₈H₈), 1, reacts with two equiv of 4,4′-dimethyl-2,2′-bipyridine (Me₂bipy) and 2 equiv of 2,2′-bipyridine (bipy) to form 2 equiv of (η⁵-C₅Me₅)(η⁸-C₈H₈)U(Me₂bipy-κ²N,N′) and (η⁵-C₅Me₅)(η⁸-C₈H₈)U(bipy-κ²N,N′), respectively. X-ray crystallography, infrared spectroscopy, and density functional theory calculations indicate that the products are best described as U⁴⁺ complexes of bipyridyl radical anions. Hence, only one of the (C₈H₈)²⁻ ligands in 1 acts as a reductant and delivers 2 electrons per equiv of 1. Since the reduction potentials of uncomplexed (C₈H₈)²⁻, Me₂bipy, and bipy are −1.86, −2.15, and −2.10 V vs SCE, respectively, it is likely that prior coordination of the bipyridine reagents enhances the electron transfer.     

Co-function of C3-and C4-photosynthetic pathways in C3, C4 and C3-C4 intermediate Flaveria species

The potential for C₄ photosynthesis was investigated in five C₃-C₄ intermediate species, one C₃ species, and one C₄ species in the genus Flaveria, using ¹⁴CO₂ pulse-¹²CO₂ chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating ¹⁴CO₂ into the C₄ acids malate and aspartate, following an 8-s pulse. The proportion of ¹⁴C label in these C₄ products ranged from 50–55% to 20–26% in the C₃-C₄ intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, ¹⁴CO₂ into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C₄ photosynthesis among the intermediate species based on the apparent rate of conversion of ¹⁴C label from the C₄ cycle to the C₃ cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C₄-cycle products and an increase in percentage label in C₃-cycle products during chase periods with ¹²CO₂, although the rate of change was slower than in the C₄ species, F. palmeri. In these C₃-C₄ intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C₃-C₄ intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C₄-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C₄ and C₃ cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C₃ species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C₄-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O₂, the absorbed quantum yields for CO₂ uptake (in mol CO₂·[mol quanta]^-1) averaged 0.053 in F. cronquistii (C₃), 0.051 in F. trinervia (Spreng.) Mohr (C₄), 0.052 in F. ramosissima (C₃-C₄), 0.051 in F. anomala (C₃-C₄), 0.050 in F. linearis (C₃-C₄), 0.046 in F. floridana (C₃-C₄), and 0.044 in F. pubescens (C₃-C₄). In 2% O₂ an enhancement of the quantum yield was observed in all of the C₃-C₄ intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O₂ were intermediate in value to the C₃ and C₄ species, indicating a co-function of the C₃ and C₄ cycles in CO₂ assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O₂ presumably reflect an ineffcient transfer of carbon from the C₄ to the C₃ cycle. The response of the quantum yield to four increasing O₂ concentrations (2–35%) showed lower levels of O₂ inhibition in the C₃-C₄ intermediate F. ramosissima, relative to the C₃ species. This indicates that the co-function of the C₃ and C₄ cycles in this intermediate species leads to an increased CO₂ concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O₂.Abbreviations PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - RuBP ribulose-1,5-bisphosphate     

Microbial fatty acid specificity

Strains ofRhodotorula sp.,Candida spp. andLangermania sp. cultivated on polyunsaturated oil preferentially incorporated more unsaturated fatty acids. These fatty acids were used mainly for growth needs whereas the saturated ones accumulated in the microbial cell. The cellular oil and the remaining oil in the culture had a lower degree of unsaturation as compared to the initial oil, and a modified fatty acid composition.Candida lipolytica, in a chemostat continuous culture, incorporated C₁₈ fatty acids in the order of C_18:3>C_18:2>C_18:1>C_18:0, and accumulated mostly the saturated ones. The specific productivity of the cellular oil and of the oil remaining in the culture medium was 0.036 and 0.487 gg⁻¹ h⁻¹, respectively, at dilution rateD=0.2/h.     

(+)-Abscisic Acid and Two Compounds Showing Chlorophyll Degradation Activity in Cuscuta pentagona Engelm

The purified polyethylene glycol (PEG) dehydrogenase from cells of a synergistic mixed culture of Flavobacterium and Pseudomonas species showed a similar absorption spectrum to those of other quinoproteins reported so far. The prosthetic group of the PEG dehydrogenase after extraction with cold methanol and purification by DEAE-Sephadex A-25 column chromatography and Sephadex G-25 gel filtration showed the same elution profiles as those of authentic pyrrolo-quinoline quinone (PQQ). Absorption and fluorescence spectra of the purified prosthetic group and its prosthetic group capability for glucose dehydrogenase indicated that it was identical with authentic PQQ.

The enzyme was induced during bacterial cell growth on a medium containing PEG 6000 as a sole source of carbon. The purified enzyme oxidized primary alcohols of C₂-C₁₆ and the corresponding aldehydes of C₄-C₇. The enzyme also reacted with nonionic surfactants containing PEG residues. The enzyme reduced 2,6-dichlorophenolindophenol (DCIP) and the Km value for DCIP was calculated to be 1.4 × 10^?4m. The DCIP reductase activity was inhibited by carbonyl reagents like semicarbazide, hydrazine, hydroxylamine and 1,4-benzoquinone. 1,4-Benzoquinone inhibited the DCIP reductase activity competitively as to DCIP.     

Paleotemperature response to monsoon activity in the Japan Sea during the last 160 kyr

Paleo-sea-surface temperatures in the northeastern- and southeastern-parts of the Japan Sea were reconstructed for the last 160 kyr using alkenone temperatures (U^K′₃₇-temperatures). U^K′₃₇-temperatures at two sites show distinct glacial–interglacial changes during the last 160 kyr except for the interval corresponding to middle MIS 3 to MIS 2. On orbital-timescales, U^K′₃₇-temperature tends to be high during MIS 5e, MIS 5c, and MIS 5a, which coincides with the intervals of stronger East Asian summer monsoon activity. The amplitude of temperature fluctuations in the Japan Sea is significantly higher than those in the neighboring seas. We suggest that the SST variation was amplified by the increasing source water (Kuroshio water) temperature and the changes in the volume transport of the Tsushima Warm Current (TWC) and/or the north–south oscillation of the sub-polar front position within the Japan Sea. Millennial-scale temperature fluctuations in the Japan Sea show that the temperature at the northern site was higher than that at the southern site during warmer periods of MIS 5, which is called “temperature reversal.” By analogy with modern oceanography, the temperature reversal could reflect the enhanced volume transport of the TWC and the spatial relationship between the studied site and the branches of the TWC, which is an essential factor in north–south temperature reversal around the eastern Japan Sea. Temperature drops were found at 114 ka, 111 ka, 93 ka, 87 ka, and 77 ka in MIS 5. Those events were associated with an increase in organic carbon and alkenone contents and can be correlated with the abundance peaks of ice-rafted debris (IRD) at Site GH05-1208 in the northern Japan Sea, suggesting that the surface water was cooled by enhanced mixing and consequent upwelling in a stronger winter monsoon regime.     

Evidence for Deuterium Retention in the Products after Enzymatic C-C and Ether Bond Cleavages of Deuterated Lignin Model Compounds

The mechanism of C-C and ether bond cleavages of C_α-or C_β-deuterated β-O-4 and β-l lignin substructure models and the vicinal diol compounds catalyzed by the enzyme system from Phanerochaete chrysosporium culture was investigated. The enzymatic oxidation of β-O-4 lignin model compounds in the presence of H₂O₂ and O₂ yielded C₆-C_α-derived benzaldehyde, and C_β-C_γ-derived product together with the arylglycerol product. Likewise, the β-l models and the diol compounds also underwent the C-C bond cleavage, yielding C₆-C_β-derived benzaldehyde and the arylglycol product. The results demonstrated that the d-labels at C_α and C_β of the substrates were retained in the products after the C_α-C_β and ether bond cleavages.     

Phosphoenolpyruvate Carboxylase Purified from Leaves of C3, C4, and C3-C4 intermediate species of Alternanthera: Properties at Limiting and Saturating Bicarbonate

Phosphoenolpyruvate carboxylase (PEPC) was purified from leaves of four species of Alternanthera differing in their photosynthetic carbon metabolism: Alternanthera sessilis (C₃), A. pungens (C₄), A. ficoides and A. tenella (C₃-C₄ intermediates or C₃-C₄). The activity and properties of PEPC were examined at limiting (0.05 mM) or saturating (10 mM) bicarbonate concentrations. The V_max as well as K_m values (for Mg²⁺ or PEP) of PEPC from A. ficoides and A. tenella (C₃-C₄ intermediates) were in between those of C₃ (A. sessilis) and C₄ species (A. pungens). Similarly, the sensitivity of PEPC to malate (an inhibitor) or G-6-P (an activator) of A. ficoides and A. tenella (C₃-C₄) was also of intermediate status between those of C₃ and C₄ species of A. sessilis and A. pungens, respectively. In all the four species, the maximal activity (V_max), affinity for PEP (K_m), and the sensitivity to malate (K_I) or G-6-P (K_A) of PEPC were higher at 10 mM bicarbonate than at 0.05 mM bicarbonate. Again, the sensitivity to bicarbonate of PEPC from C₃-C₄ intermediates was in between those of C₃- and C₄-species. Thus the characteristics of PEPC of C₃-C₄ intermediate species of Alternanthera are intermediate between C₃- and C₄-type, in both their kinetic and regulatory properties. Bicarbonate could be an important modulator of PEPC, particularly in C₄ plants. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lipid synthesis by <Emphasis Type="Italic">Geomyces pannorum</Emphasis> under the impact of stress factors

Lipogenic activity and fatty acid composition of two strains of Geomyces pannorum were studied in the course of fungal growth. The strains were isolated from an Arctic cryopeg lens (VKM FW-2241) and from Central Russia (VKM F-3808). The adaptive reactions in both strains towards the temperature decreasing to 2°C involved intensification of the fatty acid desaturation. The degree of lipid unsaturation increased mainly due to a higher amount of α-linolenic acid (α-C_18:3) especially in the case of strain VKM FW-2241. Elevated NaCl concentration in the medium enhanced the level of linoleic acid (C_18:2) which apparently played a specific role in osmoprotection. Strain VKM FW-2241 was more tolerant to increased salinity than strain VKM F-3808. Almost complete inhibition of the growth of strains VKM F-3808 and VKM FW-2241 occurred at salinity of 10 and 20%, respectively; however, the viability of the strains was not affected. Under the combined effect of high salinity and hypothermia, the ratio between C_18:2 and α-C_18:3 acids was intermediate, indicating that these acids were involved in two adaptation mechanisms. The inhibition of fungal growth under stress was found to result in lipid overproduction. An increased pool of energy-rich lipids in fungi possibly contributes to their strategy of cell survival.     

C3-C4 PHOTOSYNTHESIS IN THE GENUS MOLLUGO: STRUCTURE,PHYSIOLOGY AND EVOLUTION OF INTERMEDIATE CHARACTERISTICS

The genus Mollugo has been reported to have species which are C₄ plants and a C₃-C₄ intermediate. In the present paper, we report on the anatomy and photosynthetic physiology of three additional species in the Molluginaceae, M. pentaphylla, M. nudicaulis, and M. lotoides, all of which possess some anatomical and physiological features of both C₃ and C₄ plants. Most notable among the variable C₃-C₄ features are C₄-like bundle sheath cells, along with a C₃-like arrangement of palisade and spongy parenchyma. M. nudicaulis appeared to have lower photorespiration based on its CO₂ compensation point and lower oxygen sensitivity of photosynthesis. The occurrence of polyploidy within this group of plants and its relationship to lower photorespiration or evolution of these species is discussed.     

An examination of the advantages of C3-C4 intermediate photosynthesis in warm environments

Abstract. The photosynthetic responses to temperature in C₃, C₃-C₄ intermediate, and C₄ species in the genus Flaveria were examined in an effort to identify whether the reduced photorespiration rates characteristic of C₃-C₄ intermediate photosynthesis result in adaptive advantages at warm leaf temperatures. Reduced photorespiration rates were reflected in lower CO₂ compensation points at all temperatures examined in the C₃-C₄ intermediate, Flaveria floridana, compared to the C₃ species, F. cronquistii. The C₃-C₄ intermediate, F. floridana, exhibited a C₃-like photosynthetic temperature dependence, except for relatively higher photosynthesis rates at warm leaf temperatures compared to the C₃ species, F. cronquistii. Using models of C₃ and C₃-C₄ intermediate photosynthesis, it was predicted that by recycling photorespired CO₂ in bundle-sheath cells, as occurs in many C₃-C₄ intermediates, photosynthesis rates at 35°C could be increased by 28%, compared to a C₃ plant. Without recycling photorespired CO₂, it was calculated that in order to improve photosynthesis rates at 35°C by this amount in C₃ plants, (1) intercellular CO₂ partial pressures would have to be increased from 25 to 31 Pa, resulting in a 57% decrease in water-use efficiency, or (2) the activity of RuBP carboxylase would have to be increased by 32%, resulting in a 22% decrease in nitrogen-use efficiency. In addition to the recycling of photorespired CO₂, leaves of F. floridana appear to effectively concentrate CO₂ at the active site of RuBP carboxylase, increasing the apparent carboxylation efficiency per unit of in vitro RuBP carboxylase activity. The CO₂-concentrating activity also appears to reduce the temperature sensitivity of the carboxylation efficiency in F. floridana compared to F. cronquistii. The carboxylation efficiency per unit of RuBP carboxylase activity decreased by only 38% in F. floridana, compared to 50% in F. cronquistii, as leaf temperature was raised from 25 to 35°C. The C₃-C₄ intermediate, F. ramosissima, exhibited a photosynthetic temperature temperature response curve that was more similar to the C₄ species, F. trinervia, than the C₃ species, F. cronquistii. The C₄-like pattern is probably related to the advanced nature of C₄-like biochemical traits in F. ramosissima The results demonstrate that reductions in photorespiration rates in C₃-C₄ intermediate plants create photosynthetic advantages at warm leaf temperatures that in C₃ plants could only be achieved through substantial costs to water-use efficiency and/or nitrogen-use efficiency.     

Surface wax of Andreaea and Pogonatum species

The mosses Andreaea rupestris, Pogonatum aloides and P. urnigerum contain surface waxes in amounts of 0.05–0.12% dry wt. The waxes consisted of esters (C₃₈-C₅₄), primary alcohols (C₂₀-C₃₂), free fatty acids (C₁₆-C₃₀), and alkanes (C₂₁-C₃₁). Additionally, aldehydes (C₂₂-C₃₀) were major constituents in the wax of P. urnigerum. The classes and their chain length distributions in the surface waxes of these mosses are comparable to those of epicuticular waxes of higher plants.     

Effect of amaranth on the growth of Rhizobium and Bradyrhizobium strains

The growth rate of different strains of Bradyrhizobium and Rhizobium was studied in media containing amaranth seed meal instead of yeast extract. Results obtained in erlenmeyer flasks and stirred fermenters show that both Bradyrhizobium japonicum strains E109, E110, 5019, 587 and Rhizobium melilotistrains B36, B323, B399, Lq₂₂, Lq₄₂, Lq₅₁ and U₃₂₂, grow satisfactorily in amaranth seed meal medium. Cell count obtained for the strains tested was greater than 4 × 10¹⁰ viable cells.ml^–1. Amaranth seed meal (4 g.l^–1) is a suitable component for culture media that can be used instead of yeast extract.